In active matrix liquid crystal displays (AMLCD) and active matrix organic light emitting displays (AMOLED), there are requirements of conductive layers for different functionalities. For example, a metal layer is needed for the scan line and another metal layer is needed for the data line. These two lines cross over each other and cannot be formed during the same metal level steps. The conductivity of the metal lines for the data and scan lines is very critical and cannot be made from relatively low conductivity transparent material because of the conductivity requirement. Also, a transparent conductive layer is needed as the electrode for transmissive LCDs or bottom emitting OLEDs. It is not easy to combine or form the transparent conductor with the other metal lines. Each of the metal lines needs to be patterned in separate lithographic steps and contributes to the number of mask levels. Also, in the fabrication of AMLCDs and AMOLEDs there is another mask level, used in the formation of a spacer (in the case of an AMLCD), or a bank (in case of an AMOLEDs). It will be understood that banks or spacers are used to separate various layers in a complete display, e.g. a backplane from an emission layer. Each mask level in a process adds to the complexity and cost of the process.
More specifically, it has been noted that IPS (in-plane-switch) LCDs have become popular because of their wide viewing angle, insensitivity to finger-touching the viewing screen and better contrast. The insensitivity feature is important because many of the modern devices are at least partially controlled by touching the viewing screen. The problem with the IPS type of LCDs is that two patterned transparent electrodes are needed which results in a requirement of seven (7) patterning steps. This invention builds on the novel fabrication process for AMLCDs and AMOLEDs of the parent application in which the number of mask levels is reduced and reduces the number of mask levels required in the fabrication process of metal-oxide based TFT backpanels for IPS LCDs.
Accordingly, it is an object of the present invention to provide a new and improved fabrication process for metal-oxide based TFT backpanels for IPS LCDs in which the number of mask levels is reduced.
It is another object of the present invention to provide a new and improved metal-oxide based TFT backpanel for IPS type of LCDs which is more compact and includes fewer layers of material.
It is yet another object of the present invention to provide a new and improved metal-oxide based TFT backpanel for IPS LCD with reduced power consumption.